Another chance to see the moon below Leo

True, Leo's lion figure (as the dots are connected here) takes a fairly dark sky to see, and the moonlight won't help. But Regulus and especially Saturn will be easy even from the city.

This is a monthly column, and it's no coincidence that the moon is back in nearly the same place a month after last time. The word "month" comes from "moon." A month is about how long the moon takes to orbit the Earth - or from our Earthly point of view, to circle the sky and go through its whole cycle of phases.

But not exactly. In the calendar on your desk, the months average about 30.4 days long. However, the lunar month is about 29.5 days long. That difference of just under a day means that the moon's phases drift out of synch with the modern calendar. The months you live by are no longer connected to the moon. This is a very good thing, and thereby hangs a tale. It's a tale that has also, over the centuries, caused deep crises in religious faith.

Three great astronomical cycles - the day, the month, and the year - have governed people's ordering of time throughout history. The day is one rotation of the Earth. The month is one cycle of the moon. And the year is one revolution of Earth around the sun.

Since prehistoric times, nearly every culture has considered these cycles to be a sort of cosmic clockwork built by the Creator to mark out the cycles of nature and human life. The problem is that its gears don't mesh. Each one of the three spins along on its own, disconnected from the others. So every calendar that attempts to interrelate them, as if they were part of a single plan, becomes an ever-more-complicated mess of approximations and kludges.

The year, for instance, does not contain 365 days. It contains 365.24218967 days, with the decimal places continuing on. So if you put 365 days in your calendar, the calendar will eventually drift away from the actual seasons. To address this problem, in 46 B.C. Julius Caesar declared that every fourth year would have a leap day, giving that year 366 days.

That worked well enough for a while, but it defined the calendar year as exactly 365.25 days. Which it's not. By 1582 enough error had built up that Pope Gregory jumped the calendar forward by 11 days and declared that henceforth, no leap day would occur in whole-century years unless the year is divisible by 400. This kludge is still the rule; it's why 2000 was a leap year but 2100 won't be. This "Gregorian" calendar defines the year as 365.2425 days. Which it's not, but it's close enough to last as long as anyone is planning for yet.

And the month? It's disconnected from both the day and the year. A lunar month contains 29.530588853 days, and the number is gradually changing. A year contains 12.36826639 lunar months, also changing. That hardly makes for clean clockwork math. Nevertheless, since ancient times people have attempted to use lunar months as well as Earthly days and solar years. The price is having even more-awkward, more-irreconcilable calendars that in some cases don't even reliably predict dates in the future.

Wisely, the Western world long ago abandoned the natural month altogether, aside from a few traditional purposes such as calculating the date of Easter. Our 12 familiar months are convenient fakes. They're artificial dummy months, as if to keep a sentimental illusion of connection to the real months of the moon.

Why are these three cycles such a pathetic mess? Contrary to humanity's assumption since forever, they were not intelligently designed. They resulted from the random, natural processes of how the solar system fell together at its formation 4.6 billion years ago (and various random perturbations since then), like stars and planets everywhere. These large-scale happenstances show no more planning than swirls of dust in the wind. People have lost their faith over less.

Alan M. MacRobert is a senior editor of Sky & Telescope magazine in Cambridge (SkyandTelescope.com). His Star Watch column appears the first Saturday of every month.